482 E. O. ULRICII REVISION OF THE PALEOZOIC SYSTEMS 



deposits, suggest brackish, lagoon, and possibly lacustrine habitats. These 

 may therefore be considered in connection with non-marine fossils and as 

 similarly indicating accomplished or impending sea withdrawal; but the 

 evidence of the Eopaleozoic species on this point is far from decisive. 



FOSSIL FAUNAS AND FLORAS 



The terms faima and flora, as generally accepted, are used in two 

 broad senses, a stratigraphic and a biologic. Several distinguishable 

 meanings are included in the second. The fossil species found in any 

 division of the stratigraphic column constitute the known fauna or flora 

 of that stage. These associations may be referred to by the names of the 

 stratigraphic divisions in which they are found, or they are named from 

 some characteristic genus or species. We have then a Cambrian, an Ordo- 

 vician, a Devonian, and other faunas of similar rank; or, referring to 

 faunas of lesser rank, the Niagaran fauna, the Clinton fauna, and the 

 Eochester shale fauna. Then we may speak of the Glossopteris or Ganga- 

 mopteris flora, the Fusipira fauna, and the Manticoceras intumescens 

 fauna. Associations of animals of still lower rank are often distinguished 

 as faunules. Only those of the first rank, as the Ordovician fauna, are 

 truly world-wide in distribution, and for these only the term has the 

 single stratigraphic significance. In those of the second to the lowest 

 order a geographical or provincial significance of the term becomes more 

 and more prominent. Examples of its use in the systematic biological 

 sense would be a graptolite fauna or a crinoid fauna, while such expres- 

 sions as tlie Spergen fauna, the Hamilton fauna, or the Tropidoleptus 

 fauna, when applied to other appearances of such faunas than the first 

 described, suggest the biologic sense as much as the stratigraphic. Finally, 

 we speak of littoral, pelagic, and abyssmal faunas, or of marine, brackish, 

 lacustrine and land faunas, or of mountain, swamp, etcetera, floras. 



Theoretically, and as a rule, the distribution of a faulia is in proportion 

 to the time value of the stratigraphic unit to which it is credited. But 

 there are many notable exceptions of relatively wide-ranging faunas in 

 thin formational units, and these are of exceptional importance in strati- 

 graphic taxonomy. Such faunas occur at times of great sea transgression 

 and resulting confluence of continental basins, which at other times were 

 occupied by distinct faunas. Some of the Black Eiver and the Eich- 

 mondian faunas, as described in Part I of this work, and the New Scot- 

 land Helderbergian fauna are especially noteworthy examples because 

 their areal distribution transgresses boundaries of commonly distinct 

 provinces. Certain pelagic or planktonic faunas, notably the graptolite 



